In conventional apparatus for producing a continuous film of thermoplastic material, either as part of an extrusion coating or laminating process or to cast a continuous film, it is essential that the film be chilled as promptly as possible in order to maintain its extruded dimensions if it is to remain an independent film, or to set it in bonded relation to a web or between webs if it is used as a coating or adhesive layer. This is conventionally effected by extruding the film directly onto the surface of a drum-type roll which is hollow, and therefore includes hollow journals, so that a coolant (water) can be continuously circulated therethrough.
Such a chill roll is the largest, the heaviest, the most expensive and the most easily damaged component in the entire line of related apparatus. Its surface characteristics are critical to the quality of the plastic film whenever that film is used as a coating or as a separate product, and it therefore has a highly polished surface finish, which may be either chrome plated, matte finished, or provided with an embossed surface to be reproduced on the film. It is therefore of great importance that this surface be provided with maximum protection against injury, such as is most likely to occur during removal and replacement of the chill roll.
As an example of the practical problems involved in the handling of chill rolls, the assignee of this invention manufactures chill rolls as large as 36 and 40 inches in diameter, which have face widths as large as 180 inches, and which weigh as much as 10,000 pounds. Prior to the present invention, however, all apparatus known to the assignee thereof which incorporate chill rolls have no provision for the handling of such roll during removal and replacement except by means of an overhead crane and chain hoists. Such technique, however, involves high risks of damaging the roll surface, especially as the roll is being lifted away from or lowered back into its operating position and may therefore very easily swing into contact with associated parts of the apparatus.